Glass conductivity and temperature probe

ABSTRACT

A device for measuring the conductivity and/or temperature of glass in molten state. A probe including a hollow elongated member of nonconductive material has a pair of spaced external bands of conductive material near one end with an internal lead from each band extending to the other end of the elongated member. The leads are connected with power input means and an AC to DC converter, the latter of which is connected with a voltage readout to supply direct voltages thereto which are indicative of the conductivity of the molten glass between the bands on the probe. In addition, a thermocouple is positioned within the elongated member at the end with the bands thereon with leads therefrom being connected with a temperature readout that is externally positioned with respect to the probe.

UnitedStates Patent Jelinek et al.

[151 3,657,640 [451 Apr. 18, 1972 [54] GLASS CONDUCTIVITY ANDTEMPERATURE PROBE [72] Inventors: James W. Jelinek, Lancaster, Ohio;Joseph J. Kozlowski; Jack E. Gooding, both of Muncie, Ind.

[73] Assignee: Ball Corporation, Muncie, lnd. [22 Filed: Feb. 5, 1969[21] Appl. No: 796,682

[52] US. Cl ..324/30 R, 73/344, 324/30 A, 324/65 P [51] Int. Cl ..G01r27/42, GOlr 27/02 [58] Field of Search ..324/30, 65, 65 P, 119; 73/343,73/3435, 344

[56] References Cited UNITED STATES PATENTS 2,328,853 9/1943 Sherrard..324/65 X 2,526,636 10/1950 Colman ..324/30 X 3,152,303 10/1964 Lary etal.. .....324/65 X 3,209,249 9/1965 Warfield .....324/65 X 3,302,1021/1967 Lace ..324/65 X 1,287,970 12/1918 Greinacher et a1. ...324/119 X1,715,446 6/1929 Bossart ..324/119 X 3,278,844 10/1966 Belletal ..324/65OTHER PUBLICATIONS Rosenthal, R., Solution Conductivity Measurement;Instruments; Vol. 23; No. 7; July 1950; pp. 664- 669.

Primary ExaminerRudolph V. Rollinec Assistant Examiner-Emest F. KarlsenAttorney-Campbell, Harris & ORourke [5 7] ABSTRACT A device formeasuring the conductivity and/or temperature of glass'in molten state.A probe including a hollow elongated member of nonconductive materialhas a pair of spaced external bands of conductive material near one endwith an internal lead from each band extending to the other end of theelongated member. The leads are connected with power input means and anAC to DC converter, the latter of which is connected with a voltagereadout to supply direct voltages thereto which are indicative of theconductivity of the molten glass between the bands on the probe. Inaddition, a thermocouple is positioned within the elongated member atthe end with the bands thereon with leads therefrom being connected witha temperature readout that is externally positioned with respect to theprobe.

4 Claims, 4 Drawing Figures CONDUCTIVITY POINT 39 READOUT TEMPERATUREREADOUT 45 AC TO DC 37 CONVERTER 1000 Hz 18 v 50 mo 32 I 4o 25CAPACITANCE 53 37 SELECTOR POWER INPUT PATENTEDAPR 18 I972 3,657. 640SHEET 10F 2 4/ l CONDUCTIVITY POINT READOUT TEMPERATURE T READOUT 45 ACTO 00 15 5/ CONVERTER 32 #7 2 CAPACITANCE 35 37 SELECTOR POWER INPUTI000 Hz l8v 50 m0 INVENTORS JAMES w. JELINEK Q BY JOSEPH J. KIOZLOWSKI vJACK E. GOODING GLASS CONDUCTIVI'I'Y AND TEMPERATURE PROBE BACKGROUND OFTHE INVENTION 1. Field of the Invention This invention relates to aglass conductivity and temperature probe and, more particularly, relatesto a device for mea- 1 s'uring the viscosity of glass in molten state.

2. Description of the Prior Art It is oftentimes desirable to measurethe conductivity of molten glass. Such measurement can be used to goodadsince conductivity and temperature are related to glass viscosity. Inaddition to serving as a process control link, such a device can also beutilized as an early warning system to detect such things as errors inglass batch formulations.

While devices have been known and/or utilized previously to determineconductivity or resistivity of molten glass as well as todetermine thetemperature of such glass, these devices have not proved to becompletely successful for all purposes.

I In some of the devices taught by the prior art, for example,

separate pairs of electrodes have commonly been required, with one setbeing connected with the power supply and the other set being connectedwith readout equipment in order to measure conductivity. In other priorart devices, difficulty has been experienced because of the inability ofthe device to handle a sufiicient range of temperature encountered, due,at least in part, to a lack of sufficient circuitry for accurateconductivity readout which, for example, can be caused by phase shiftsdue to the changed capacitance of the probe under varying conditions. Inaddition, still other devices have proved to be so unwieldly orcomplicated that dependability and/or versatility were sacrificed.

SUMMARY OF THE INVENTION This invention provides an improved device formeasuring the conductivity of glass in molten state wherein a probehaving metallic bands thereon is utilized as a conductivity measur ingcell, with this cell being connectable to both a power supply and areadout device. This invention also provides, as a part of the device,means for measuring the temperature of molten glass and a readout forthe same so that the device is suitable for monitoring glass viscosity.

It is therefore an object of this invention to provide an improveddevice for measuring the conductivity of glass in molten state.

It is another object of this invention to provide an improved device formeasuring both the conductivity and temperature of molten glass wherebythe viscosity of said glass can be monitored.

It is another object of this invention to provide an improved measuringdevice having one pair of electrodes connectable with both a powersupply and a readout device.

It is still another object of this invention to provide an improveddevice including a probe having bands thereon immersible in molten glassto measure the conductivity of said glass.

It is yet another object of this invention to provide an improved devicefor measuring the conductivity of molten glass including a probe withtwo electrodes thereon connectable with a power supply of predeterminedfrequency and voltage and to an AC to DC converter, the direct voltageoutput of which is indicative of the conductivity of said molten glass.

It is still another object of this invention to provide an improvedconductivity measuring device having accurate readout. 4

It is yet another object of this invention to provide an improvedconductivity measuring device having phase shift compensation circuitrywhereby said readout is accurate over a broad range.

With these and other objects in view which will become ap parent to oneskilled in the art as the description proceeds, this invention residesin the novel construction, combination and arrangement of partssubstantially as hereinafter described and more particularly defined bythe appended claims, it being understood that such changes in theprecise embodiment of the hereindisclosed invention are meant to beincluded as come within the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrate acomplete embodi ment of the invention according to the best mode so fardevised for the practical application of the principles thereof, and inwhich:

FIG. 1 is a perspective view of the probe of this invention;

FIG. 2 is an illustrative view showing the use of the probe of FIG. 1immersed in molten glass;

FIG. 3 is a combined block diagram and probe electrical diagram of thedevice of this invention; and

FIG. 4 is a schematic block and circuit diagram of the con ductivityprobe as shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,the numeral 7 indicates generally a probe suitable for immersion inmolten glass. As shown best in FIG. 1, probe 7 includes an elongatedmember 8 of nonconductive material having a pair of bands 9 and 10 atone end thereof, said bands being of conductive material. With respectto lower band 9, it is to be noted, as shown in FIG. 1, that this bandis preferably a cap which goes over the end of the probe.

While any electrically nonconductive material may be used, so long asthe material will withstand the expected tempera ture of the moltenglass, it has been found that recrystalized alumina can, for example, beutilized to good advantage. The bands 9 and 10 must be of electricallyconductive material and while any such material suitable forwithstanding the temperatures to be encountered may be utilized, it hasbeen found that pure platinum can be used to good advantage.

Elongated member 8 of probe 7 is preferably of very small diameter so asnot to interfere with the flow of molten glass and is preferably aboutone-fourth inch in diameter. The length of the elongated member will bedependent, of course, upon desired use. It has been found, however, thanan elongated member about 18 inches in length can be used to goodadvantage. Metallic bands 9 and 10 are preferably spaced about one-halfinch part to create a measuring cell between the two bands with aconductivity cell factor of about 0.486.

As shown in FIG. 3, the bands 9 and 10 are each connected with adifferent lead 14 and 15, which extend through the hollow elongatedmember 8 to the end 16 opposite the end with the bands where the leadspreferably terminate at a junction block 17 as shown in FIG. 1. As alsoindicated in FIG. 3, the elongated member 8 may also have an internalthermocouple 18 at the end of the elongated member so as to bepositioned within cap 9, with the two leads from the thermocouple beingcoupled by leads 20 and 21 to end 16 of the elongated member.

As shown in FIG. 2, the probe may be fastened or inserted through asuitable opening 22 in a molten glass retainer which may, for example,be a forehearth 23 through which molten glass 24 is flowing, so that theend of the probe with the bands thereon is immersed into the moltenglass. For the probe, as shown in the drawing, it is only necessary thatthe probe be immersed into the glass a distance of about 2 inches. Asalso shown in FIG. 2, a sleeve 25 which may be of the same material asthe elongated member 8 may be placed over the probe to give extraprotection thereto. If the probe is to remain in the molten glass forany length of time, the probe is preferably fastened in place byfastening means 26, which can, for example, clamp the probe in position.

As shown in FIG. 3, power input terminals 28 and 29 are provided, whichinput terminals may be connected to power input 30. Power input 30provides an AC signal having a frequency of 1,000 Hz. with an amplitudeof about 18 volts peak-to-peak at about 50 milliamps.

The X factor of the measuring cell combined with the glass resistanceresults in a cell resistance of only a few ohms (lessthan 10 ohms).Since the resistance of the remaining bridge circuit is suflicientlyhigh (several thousand ohms), changes in the cell resistance will notappreciably affect current flow. Current in the circuit can beconsidered constant as long as the applied voltage remains constant. Theelectrical resistance of the molten glass is then determined by thevoltage drop across the measuring cell divided by the current in thecircuit.

As shown in FIG. 3, power input terminal 28 is connected to the twoinputs to an AC to DC converter 31 one connection being through resistor32, and the other connection being through resistor 33 and variableresistor 37, resistor 32 having a value of 500 ohms, resistor 33 havinga value of 2K ohms, and variable resistor 37 having a value of -50 ohms.AC to DC converter 31 is required to demodulate the 1,000 Hz. drop inorder to determine the EMF of the measuring cell. It has been found thatthe normal range of cell voltage drop is between 100 and 500 millivoltspeak-to-peak.

The junction of resistor 32 and one input to AC to DC converter 31 isconnected by means of lead 34 to lead 14 from the probe (and thus isconnected to cap 9). Lead 15 coming from band of the probe is directlyconnected by means of lead 35 to power input 29 (grounded), and isconnected to the end of variable resistor 37 opposite resistor 33 sothat variable resistor 37 is used for adjustment of the readout forconductivity measurement.

As also shown in FIG. 3, the output from the AC to DC converter 31 iscoupled to conductivity readout 39, which readout receives the directvoltage output from the AC to DC converter, and is indicative of theconductivity of glass measured by the measuring cell formed by bands 9and 10. Readout 39 can be, for example, an ammeter, as shown in FIG. 4,or a recorder such as an Esterline Angus recorder having ranges from 1millivolt upward.

The conductivity probe represents a complex cell when immersed in moltenglass, the total reactance of which is dependent upon both resistanceand capacitance which vary with the electrical conductivity of theglass. The changing capacitance of the measuring cell results in achange in electrical phase angle of the cell relative to the remainderof the bridge circuit made up of the measuring cell and resistors 32, 33and 37. The changing phase angle, in turn, interferes with accurateconductivity measurement since a meter null point cannot be reached,which is a necessary prerequisite for accurate conductivity measurement.This problem has been overcome, however, by the addition of acapacitance selector 40 connected between ground and the movablecontactor of variable resistor 37, as shown in FIG. 3. The purpose ofthis selector is to place additional capacitance in the circuit asneeded, the added capacitance being unlike the capacitance of the probedue to the multiplication factor of the bridge circuit.

If a thermocouple is included in the probe, the leads 20 and 21therefrom are connected through leads 41 and 42, respectively, to apoint temperature readout 43, as also shown in FIG. 3. Readout 43 canbe, for example, a PT PT 13 per cent Rh temperature recorder.

1n the embodiment as described herein, the glass measuring cell willexhibit a resistance of from about 0 to 6 ohms, and with this design, aglass temperature change of about 250 F. will cause a change of about100 millivolts peak-to-peak, or 1 millivolt peak-to-peak per 2-% F. Itis also to be noted that the probe is not grounded electrically and willtherefore prevent blistering of the glass.

As shown in FIG. 4, power input 30 includes a constant current generator46 having a pair of transistors 48 and 49 the emitters of which areconnected through a capacitor 50 to input terminal 28. The collector oftransistor 48 is connected to a +18 volt power source (not shown) whilethe collector of transistor 49 is connected to ground. The base oftransistor 48 is connected to the +18 volt power source (not shown)through resistor 52, while the base of transistor 49 is connected toground through resistor 53, the bases of transistors 48 and 49 beingconnected together through diodes 54 and 55. The junction of the base oftransistor 49, diode 55, and resistor 53 is also connected throughcapacitor 56 to a conventional oscillator 57 providing a 1,000 I-Iz.output signal. For purposes of illustration of particular componentsthat can be utilized, transistor 48 can be a 2N17l l, transistor 49 a2N4037, capacitor 50 SO-II-Fd, resistor 52 18K, resistor 53 15K, diodes54 and 55 a 1N458, and capacitor 56 0.47 uFd.

Capacitance selector 40 includes a switch 60 the movable arm of which isconnected to the movable arm of variable resistor 37. Switch 60 selectsone of capacitors 62 through 67 (the other side of each of which isconnected to ground) to make possible nulling of the meter for accurateconductivity readout. For purposes of illustration, capacitors 62through 67 can be 0.47, 0.57, 0.68, 0.8, 0.9, and 1 #Fd, respectively,with switch 60 selecting the proper one needed in each case for nullingpurposes.

As also shown in FIG. 4, AC to DC converter 31 can include anoperational amplifier 70, the AC input to which is coupled throughresistors 71 and 72. In addition, the junction of resistor 71 and oneinput (2 as designated in FIG. 4) is connected with a +11.2 volt powersupply (not shown) through resistor 73, with the amplifier output (7 asdesignated in FIG. 4) being connected to resistor 73 through eitherresistor 74 (for multiplication by 1,000) or 75 (for multiplication by100) as determined by switch 76. A capacitor 77 is also connectedbetween pin 6 of amplifier 70 and ground. The output from the amplifieris coupled through capacitor 78 to a diode bridge with the DC outputfrom the bridge being coupled to conductivity readout 39. For purposesof illustration of particular components that can be utilized,operational amplifier 70 can be a p.A-702, resistor 71 ohms, resistor 7282 ohms, resistor 73 470K ohms, resistor 74 191K ohms, resistor 75 10Kohms, capacitor 77 1,000 #Fd, capacitor 78 0.47 uFd, and each diode ofdiode bridge 80 a 1N281.

The input to a meter such as conductivity readout 39 is shown in FIG. 4.As shown, diode bridge 80 is connected at one side directly to a 0-50 maammeter 82, and at the other side of the meter through resistors 84 and85. A capacitor 86 and meter protecting diode 87 are connected acrossmeter 82 and resistor 85. For purposes of illustration of particularcomponents that can be utilized, meter 82 can be a Simpson meter,resistor 84 K ohms, resistor 85 6.8K ohms, capacitor 86 0.1 uFd, anddiode 87 can be internal to the Simpson meter.

In operation, the probe is inserted into the molten glass and the powerinput means connected with the power source. The output from themeasuring cell will then be converted by the AC to DC converter to adirect voltage output, which may then be read out or recorded, thisoutput being a measure of the conductivity of the glass. With athennocouple included, the temperature of the glass is also determinedand may likewise be read out or recorded. By measuring both of theseparameters, glass viscosity may be continuously monitored. Since theconductivity of the glass is also affected by glass batch formulation,monitoring for errors in the glass batch can also be achieved.

From the foregoing, it can be seen that this invention provides animproved device for measuring glass conductivity, as well as providing adevice for continuous monitoring of glass viscosity.

What is claimed is:

l. A device for measuring the conductivity of glass in molten state,said device comprising: a probe having an elongated hollow body sectionof nonconductive material with first and second external bands ofconductive material near one end spaced from one another, and first, andsecond leads connected with said first and second bands, respectively,and extending therefrom to the other end of said body section of saidprobe; power input means adapted to be connected to a power source ofpredetermined voltage and frequency, said probe further including athermocouple within said hollow body section near the end of said probewith said bands thereon, and further characterized by temperaturereadout means connected to receive the output from said thermocouplewhereby glass viscosity is continuously monitored by continuousmeasurement of both the conductivity and temperature of said moltenglass; an AC to DC converter with first and second inputs; first andsecond resistors connected with one of said power input means at oneside and with said first and second inputs, respectively, of said AC toDC converter, said second resistor being a variable resistor; firstcircuit means connecting the junction of said first resistor and saidone input of said AC to DC converter with said first lead of said probe;second circuit means for connecting the other side of said power inputmeans with said second lead of said probe and with said second resistor,second circuit means also including variable capacitance means connectedbetween said second lead of said probe and said second input of said ACto DC converter, said variable capacitance means including a pluralityof capacitors and switching means for selectively connecting saidcapacitors in circuit; and readout means connected to receive the directvoltage output from said AC to DC converter, said readout meansindicating conductivity as measured by said bands as a measuring cellwhen immersed in molten glass.

2. A device of claim 1 wherein said elongated hollow body section has adiameter no greater than about one-fourth inch and wherein said bandsare spaced apart about one-half inch.

3. A device of claim 1 wherein said predetermined voltage is about 18volts peak-to-peak and wherein said frequency is about 1,000 Hz.

4. A device of claim 1 wherein said 'bands and said resistors each formpart of a bridge circuit.

1. A device for measuring the conductivity of glass in molten state,said device comprising: a probe having an elongated hollow body sectionof nonconductive material with first and second external bands ofconductive material near one end spaced from one another, and first andsecond leads connected with said first and second bands, respectively,and extending therefrom to the other end of said body section of saidprobe; power input means adapted to be connected to a power source ofpredetermined voltage and frequency, said probe further including athermocouple within said hollow body section near the end of said probewith said bands thereon, and further characterized by temperaturereadout means connected to receive the output from said thermocouplewhereby glass viscosity is continuously monitored by continuousmeasurement of both the conductivity and temperature of said moltenglass; an AC to DC converter with first and second inputs; first andsecond resistors connected with one of said power input means at oneside and with said first and second inputs, respectively, of said AC toDC converter, said second resistor being a variable resistor; firstcircuit means connecting the junction of said first resistor and saidone input of said AC to DC converter with said first lead of said probe;second circuit means for connecting the other side of said power inputmeans with said second lead of said probe and with said second resistor,second circuit means also including variable capacitance means connectedbetween said second lead of said probe and said second input of said ACto DC converter, said variable capacitance means including a pluralityof capacitors and switching means for selectively connecting saidcapacitors in circuit; and readout means connected to receive the directvoltage output from said AC to DC converter, said rEadout meansindicating conductivity as measured by said bands as a measuring cellwhen immersed in molten glass.
 2. A device of claim 1 wherein saidelongated hollow body section has a diameter no greater than aboutone-fourth inch and wherein said bands are spaced apart about one-halfinch.
 3. A device of claim 1 wherein said predetermined voltage is about18 volts peak-to-peak and wherein said frequency is about 1,000 Hz.
 4. Adevice of claim 1 wherein said bands and said resistors each form partof a bridge circuit.